JP7218539B2 - Coating liquid for forming surface coating layer and porous silicon laminate - Google Patents

Description

The present invention provides a coating liquid for forming a surface coating layer capable of forming a surface coating layer of an inorganic layered compound on the surface of a porous body with good adhesion without clogging the pores of the porous body, and the coating composition thereof. The present invention relates to a manufacturing method, a porous silicon laminate in which this surface coating layer is formed on the surface of a porous silicon body, and a manufacturing method thereof.

Porous silicon films have excellent properties such as a low refractive index, transparency, and electrical insulation, and are therefore used in a wide range of industrial fields. In particular, due to its low refractive index, it is applied to antireflection films, optical waveguides, and lenses. Practical use is being considered.

However, not only porous silicon films but also porous films have pores. There is a problem that the elastic material penetrates into the pores and the pores disappear.

In addition, when a porous film and other materials are attached together with an optical adhesive or pressure-sensitive adhesive, there is a problem that the low-molecular-weight compounds of the optical adhesive or pressure-sensitive adhesive permeate into the pores, causing the pores to disappear. be.
Furthermore, when a porous film is provided on the outermost surface of a member and used, fingerprints, cosmetics, chemical solutions, sweat, etc. adhere to the surface of the porous film in the usage environment and soak into the pores, There is also the problem of vacancies disappearing. Moreover, the infiltrated material cannot be easily wiped off, and remains in the pores as a contaminant.

Therefore, for example, in the field of surface treatment methods for porous bodies such as silica airgel, the inorganic layered compound is applied to the surface of the porous body by bringing the porous body into contact with a treatment liquid in which the inorganic layered compound is dispersed in a solvent. A method of forming an adsorption layer of an inorganic layered compound by adsorption has been proposed (Patent Document 1).

In Patent Document 1, phyllosilicate minerals such as montmorillonite, smectite, and hectorite are used as inorganic layered compounds. It is described that an adsorption layer of an inorganic layered compound can be formed by obtaining a plate-like substance of 100 nm, bringing the surface of the porous body into contact with the dispersion, and pulling it out of the dispersion.

As in Patent Document 1, when an adsorption layer of an inorganic layered compound is formed on the surface of a porous body, the adsorption layer has low adhesiveness to the porous body because it does not have an adhesive component. There is a problem that it peels off from the porous body in the use environment. Patent Document 1 proposes the use of an ionic polymer in order to increase the adhesive strength. Since it remains after forming a film, the porosity of the porous body changes, which affects the refractive index, and when it is intended to be used as an optical member, there is a problem that it becomes difficult to control the optical properties.

In addition, the method for forming an inorganic layered compound adsorption layer in Patent Document 1 is a method of immersing a porous body in a dispersion liquid of an inorganic layered compound. There is also a problem that it is difficult to put it into practical use because there are many restrictions on the shape of the substrate to be used.

In addition, although there is a wet coating method as a general film forming method, in Patent Document 1, a solution in which a film material is dissolved in a solvent is applied to the surface of a porous body, and the solvent is removed by evaporation to form a porous body. When forming a film on the surface of the body, it is described that it is difficult to form a film on the porous body so as to cover the surface with the film because the solution permeates into the pores of the body. .
In addition, in Patent Document 1, only the evaluation that the surface of the porous membrane is smoothed by the formation of the adsorption layer of the inorganic layered compound is performed, and the maintenance of the pores in the porous membrane after the adsorption layer is formed Evaluation of the state and evaluation of adhesion of the adsorption layer are not made.

Japanese Patent Application Laid-Open No. 2001-342016

The present invention provides a coating liquid for forming a surface coating layer capable of forming a surface coating layer of an inorganic layered compound on the surface of a porous body with good adhesion without clogging the pores of the porous body, and the coating composition thereof. It is an object of the present invention to provide a manufacturing method, a porous silicon laminate in which the surface coating layer is formed on the surface of the porous silicon body, and a manufacturing method thereof.

The inventors of the present invention have made intensive studies to solve the above problems, and found that a coating liquid containing nanosheets of an inorganic layered compound, preferably a smectite group clay mineral, to which a silicate oligomer is adsorbed is coated on the surface of a porous body. By doing so, the surface coating layer of the inorganic layered compound can be formed with good adhesion without clogging the pores of the porous body, and the present invention has been completed.
The present invention is as follows.

[1] A coating liquid for forming a coating layer on the surface of a porous body, the coating liquid for forming a surface coating layer containing an inorganic layered compound to which a silicate oligomer is adsorbed.

[2] The coating solution for forming a surface coating layer according to [1], wherein the inorganic stratiform compound is a smectite group clay mineral.

[3] A method for producing a coating liquid for forming a coating layer on the surface of a porous body, comprising a bifunctional hydrolyzable silane compound and a polymer of the hydrolyzable silane compound, and An aqueous acid catalyst solution having an acid concentration of 0.0001 to 0.01% by mass is continuously added to a hydrophilic solvent solution in which a hydrolyzable silane composition containing at least 50% by mass of a decomposed silane compound is dissolved, while stirring. The hydrolyzable silane composition is added dropwise to the hydrolyzable silane composition to carry out hydrolysis and condensation reactions, the resulting reaction solution is diluted with a solvent, and the resulting diluted solution and a dispersion solution in which an inorganic layered compound is dispersed in a dispersion medium. A method for producing a coating solution for forming a surface coating layer, characterized by mixing

[4] A porous silicon laminate comprising a laminate of a porous silicon body and a surface coating layer containing an inorganic layered compound to which a silicate oligomer is adsorbed.

[5] The porous silicon laminate according to [4], wherein the porous silicon body has a pore size of 50 nm or less.

[6] In terms of the minimum reflectance for light incident on the porous silicon laminate from the surface coating layer side, the difference between the minimum reflectance before forming the surface coating layer and after forming the surface coating layer is less than 1.0%. The porous silicon laminate according to [4] or [5], characterized in that

[7] The porous silicon laminate according to any one of [4] to [6], wherein the surface of the surface coating layer is treated with a silane coupling agent.

[8] A method for producing a porous silicon laminate according to any one of [4] to [7], wherein the inorganic A method for producing a porous silicon laminate, comprising the step of applying a surface coating layer-forming coating solution containing a layered compound and then drying the coating solution.

According to the present invention, a surface coating layer of an inorganic layered compound can be formed on the surface of a porous body with good adhesion without clogging the pores of the porous body.
According to the present invention, a surface coating layer having excellent chemical resistance, scratch resistance, penetration resistance, stain resistance, etc., can be formed with good adhesion without impairing the original optical properties of the porous silicon body. It is possible to easily form a functional film on the formed surface coating layer by a wet coating method or the like, or to laminate a glass substrate or other functional film via an optical adhesive or pressure-sensitive adhesive. can.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing one aspect of the configuration of the porous silicon laminate of the present invention. FIG. 4 is a schematic diagram showing another aspect of the configuration of the porous silicon laminate of the present invention.

Embodiments of the present invention will be described in detail below, but the present invention is not limited to the following embodiments, and can be arbitrarily changed and implemented without departing from the gist of the present invention. .

[Porous silicon body]
First, a porous silicon body suitable as a porous body for forming a surface coating layer with the coating liquid for forming a surface coating layer of the present invention will be described.
The porous body to which the present invention is applied is not limited to the porous silicon body, and may be a porous metal, a porous inorganic-organic hybrid body, or the like. However, a porous silicon body is preferable as the porous body because it has excellent properties such as a low refractive index, transparency, and electrical insulation, and has a wide range of applications and excellent practicality.

<Shape>
The shape of the porous silicon body is not particularly limited, and it can be used for bulk substrates, but it is preferably in the form of a film. Particularly when used for optical applications, it is generally used as a film (hereinafter sometimes referred to as "porous silicon layer") formed on a transparent substrate. Further, the surface of the porous silicon layer is preferably smooth, and the unevenness is preferably 5 nm or less, more preferably 3 nm or less, and most preferably 2 nm or less. If the unevenness is large, there is a possibility that the effect of preventing permeation by the surface coating layer is not sufficiently exhibited.

<Refractive index>
The refractive index of the porous silicon body is usually 1.15 or more and 1.40 or less, and is appropriately selected depending on the application. When used as an antireflection film for glass or plastic substrates, the refractive index is preferably 1.20 or more and 1.35 or less. When forming an antireflection film with a single porous silicon layer, the minimum reflectance can be brought as close as possible to 0% by selecting the refractive index of the porous silicon layer according to the refractive index of the substrate. When used for a total reflection film, the refractive index is preferably 1.25 or less, more preferably 1.20 or less, and particularly preferably 1.18 or less. The lower the refractive index, the higher the ratio of the light that is totally reflected at the interface between the transparent substrate and the porous silicon layer. Mechanical strength may decrease.

<Structure>
The structure of the porous silicon body is not particularly limited, and its pores are usually tunnel-shaped or connecting pores in which independent pores are connected, but there is no particular restriction on the detailed pore structure. In addition, by adjusting the pore size and porosity, it is possible to adjust the refractive index, dielectric constant, and density. can be done. The pore size and porosity can be adjusted by the composition and coating method of the coating liquid for forming the porous silicon layer, which will be described later.

Although the pore size of the porous silicon body is not particularly limited, the pore size is generally preferably 0.1 to 50 nm, more preferably 1 to 20 nm, and most preferably 2 to 10 nm. If the pore size is too large, for example, it is not suitable for an antireflection film formed of a thin film of about 100 nm, and defects occur on the surface of the formed porous silicon layer, and the surface unevenness increases. Haze may increase due to scattering of Moreover, there is also a problem that the mechanical strength of the porous silicon layer is lowered due to many defects.

Although the porosity of the porous silicon body is not particularly limited, the porosity is preferably 10 to 70%, more preferably 20 to 70%, and even more preferably 30 to 70%. If the porosity is too small, the refractive index will not be low, and sufficient optical properties may not be obtained. On the other hand, if it is too large, there is a risk of lowering mechanical strength, increasing haze, and lowering surface smoothness.

The pore size of the porous silicon body is measured by analyzing observation images with a transmission electron microscope (TEM) or scanning electron microscope (SEM).
Also, the porosity of the porous silicon body can be obtained from the relational expression between the porosity and the refractive index according to the Lorentz-Lorentz equation.

Although the thickness of the porous silicon layer is not particularly limited, it is preferably 30 to 5000 nm, more preferably 40 to 3000 nm, and most preferably 50 to 2000 nm for use as an optical function layer.

<Method for producing porous silicon layer>
An example of a method for producing a porous silicon layer suitable for the present invention will be described below, but the method for producing a porous silicon layer used in the present invention is not limited to the following method.

In order to form a porous silicon layer, a coating liquid for forming a porous silicon layer (hereinafter sometimes referred to as a "porous forming coating liquid") is applied to a substrate, and the obtained wet The film is cured by heat drying.
The porous-forming coating liquid is produced, for example, by adding fine silica particles to a siloxane oligomer obtained by hydrolyzing and condensing reaction of alkoxysilane, water, and an organic solvent as raw materials with the addition of a catalyst.

(Silica fine particles)
The silica fine particles are not particularly limited, and may be either agglomerated silica fine particles or non-aggregated silica fine particles. Examples include fine particles and silica fine particles composed of at least one kind of chain aggregated silica fine particles having an average primary particle size of 5 to 100 nm. These are appropriately selected depending on the purpose of the porous silicon layer to be formed.

Specific examples of aggregated silica fine particles include "Snowtex (registered trademark)-OUP" (average length: 40 to 100 nm) manufactured by Nissan Chemical Industries, Ltd., "Snowtex (registered trademark)-UP" (average length : 40 to 100 nm), “Snowtex (registered trademark) PS-M” (average length: 80 to 150 nm), “Snowtex (registered trademark) PS-MO” (average length: 80 to 150 nm), “Snow Tex (registered trademark) PS-S” (average length: 80 to 120 nm), “Snowtex (registered trademark) PS-SO” (average length: 80 to 120 nm), “IPA-ST-UP” (average length thickness: 40 to 100 nm), "Fine Cataloid F-120" manufactured by Nippon Shokubai Kasei Kogyo Co., Ltd., and the like. Specific examples of the spherical non-aggregated silica fine particles include “Snowtex (registered trademark)-O”, “Snowtex (registered trademark)-O-40” and “Snowtex (registered trademark)-” manufactured by Nissan Chemical Industries, Ltd. OL", Fuso Chemical Co., Ltd. "Quatron (registered trademark)-PL-1", "Quatron (registered trademark)-PL-3", "Quatron (registered trademark)-PL-7", and the like.

(substrate)
A transparent substrate such as glass or plastic is used as the substrate on which the porous-forming coating liquid is applied. The transparent substrate has high translucency at a certain specific wavelength, and is appropriately selected according to the use of ultraviolet light, visible light, and infrared light. The specific wavelength is not limited to the range of visible light. It is preferred to have high permeability. Generally, one having a total light transmittance of 60% or more is used.

The thickness and shape of the substrate are not particularly limited, and as long as the performance of the porous silicon layer is not affected, the substrate may have scattering or haze, or may have fine irregularities on its surface.

Plastics constituting the substrate include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), polyimide (PI), polymethyl methacrylate (PMMA), cycloolefin polymer (COP) and the like.

The surface of the base material may be surface-modified or untreated.

(Coating method)
The method of applying the porous-forming coating liquid to the substrate is not particularly limited, and includes dip coating, spin coating, die coating, spray coating, gravure coating, roll coating, curtain coating, and screen printing. method, inkjet printing method can be mentioned.

(Drying, curing method)
Drying of the wet film is performed to remove the solvent, the drying temperature is usually 50 to 80° C., and a hot air dryer or the like is preferably used. The drying time is usually 1 to 10 minutes, preferably 1 to 5 minutes.

When the transparent substrate is made of plastic, a method of irradiating ultraviolet rays in the presence of oxygen is recommended as the curing treatment in order to impart adhesion. Ultraviolet rays include near ultraviolet rays (near UV, wavelength 200 to 380 nm), far ultraviolet rays (far UV, wavelength 10 to 200 nm) and extreme ultraviolet rays (extreme UV, wavelength 1 to 10 nm), but usually far ultraviolet rays are effective. is. Examples of ultraviolet radiation sources include low-pressure mercury lamps, high-pressure mercury lamps, excimer ultraviolet (excimer UV) lamps, halide lamps, and lasers. The irradiation time of ultraviolet rays is usually 1 second to 3 minutes.

The method for producing the porous silicon layer used in the present invention is not limited to the above-described production method, and other production methods such as a mold method and a supercritical method may be used as long as the effects of the present invention are not significantly impaired. can be used.

[Surface coating layer]
Next, a method for forming a surface coating layer on a porous body such as the above porous silicon body using the coating solution for forming a surface coating layer of the present invention will be described.

The surface coating layer according to the present invention (hereinafter sometimes referred to as "the surface coating layer of the present invention") is obtained by applying the coating liquid for forming the surface coating layer of the present invention to the surface of a porous body, followed by heating. It is a layer formed by drying. By forming the surface coating layer of the present invention on the surface of a porous body, a coating liquid composition, an optical adhesive composition, or the like can be applied onto the surface coating layer. It is possible to make it difficult for the composition to pass through the porous body side, prevent the composition from permeating into the pores of the porous body, and maintain the pores of the porous body. Therefore, for example, the pores of the porous silicon layer or the like can be maintained to suppress changes in optical properties such as the refractive index.

The coating liquid for forming a surface coating layer of the present invention contains an inorganic layered compound to which a silicate oligomer is adsorbed, and is preferably a silicate oligomer produced using a composition containing an alkoxysilane, water, and an organic solvent. and an inorganic nanosheet obtained by cleaving an inorganic layered compound, which is a smectite group clay mineral, into a thin film.
Several to several tens of layers of inorganic nanosheets overlap on the surface of the porous body to cover the surface of the porous body, and play a role in preventing penetration of various materials into the pores of the porous body. It has the role of strengthening the adhesion between the inorganic nanosheets and the adhesion between the inorganic nanosheet and the surface of the porous body.

<Production of silicate oligomer solution>
Silicate oligomers are produced, for example, using a composition comprising a hydrolyzable silane compound, water, and an organic solvent.

A hydrolyzable silane compound is a silane compound having a hydrolyzable group such as an alkoxy group, an alkoxyalkoxy group, an acyloxy group, an aryloxy group, an aminoxy group, an amide group, a ketoxime group, an isocyanate group, or a halogen atom. As hydrolyzable silane compounds, monofunctional to tetrafunctional ones are known, depending on the number of hydrolyzable groups.

In the present invention, an alkoxysilane compound is preferably used as the hydrolyzable silane compound. The alkyl group of the alkoxy group (-OR) is exemplified by lower alkyl groups such as methyl group, ethyl group, propyl group and butyl group.

Representative examples of alkoxysilane compounds include dimethyldimethoxysilane (DMDMS), methyltrimethoxysilane (MTMS), tetramethoxysilane (TMOS), dimethyldiethoxysilane (DMDES), methyltriethoxysilane (MTES), and tetraethoxysilane. (TEOS) and the like. Commercially available dimethyldimethoxysilane (DMDMS) is typically a 99 wt% pure solution.

The polymer of the hydrolyzable silane compound is obtained by condensation polymerization (oligomerization) of the above monomers. In this reaction, first, a silanol group (--Si--OH) is formed by hydrolysis of the alkoxy group. At the same time, alcohol (R--OH) is produced. Subsequently, silanol groups are (dehydrated) condensed to form siloxane bonds (--Si--O--Si--O--), and this condensation is repeated to form siloxane oligomers. As the polymer of the alkoxysilane compound, a polymer of tetramethoxysilane in which R is a methyl group or a polymer of tetraethoxysilane in which R is an ethyl group is preferable from the viewpoint of hydrolyzability and condensability of the alkoxy group. .

Structures of multimers include linear, branched, cyclic, and network structures. A tetraalkoxysilane multimer having a linear structure is represented by the following general formula (I): expressed.

RO(Si(OR) _2O ) _nR (I)
In general formula (I), R is an alkyl group, and n represents the degree of multimerization. Commonly available multimers are compositions of multimers in which n differs and therefore have a distribution of molecular weights. Incidentally, the multimerization degree is represented by the average n.

The degree of multimerization of a tetrafunctional hydrolyzable silane compound such as tetraalkoxysilane or its multimer is sometimes expressed as "silica content". The “silica content” is the mass ratio of silica (SiO ₂ ) generated from the compound, and is obtained by stably hydrolyzing the compound and measuring the amount of silica generated by firing. The "silica content" also indicates the proportion of silica produced per molecule of the compound, and is a value calculated by the following formula (II).
Silica content (parts by mass) = degree of multimerization x molecular weight of _SiO2 /molecular weight of the compound (II)

In the present invention, multimers having a multimerization degree n of usually 2-100, preferably 2-70, more preferably 2-50 are used. Since such multimers are already commercially available, it is convenient to use them. As the multimerization degree n increases, the molecular weight of the resulting silicate oligomer increases, the molecular weight distribution widens, and the viscosity increases.

Commercial products of multimers of hydrolyzable silane compounds include MKC Silicate MS51, MKC Silicate MS56, MKC Silicate MS57, and MKC Silicate MS56S (all of which are tetramethoxysilane multimers) manufactured by Mitsubishi Chemical Corporation, and methyl Silicate 51 (tetramethoxysilane multimer), methyl silicate 53A, ethyl silicate 40, ethyl silicate 48, ethyl silicate 40 and silicate 45 manufactured by Tama Kagaku Kogyo Co., Ltd. (both of which are tetraethoxysilane multimers), and the like.

In the present invention, a hydrolyzable silane composition containing a bifunctional hydrolyzable silane compound and a polymer of a hydrolyzable silane compound and containing 50% by mass or more of the polymer of the hydrolyzable silane compound is used. The proportion of polymers in this hydrolyzable silane composition is preferably 70 mass % or more.
If the proportion of polymers in the hydrolyzable silane composition is too low, it will be difficult to achieve the object of the present invention. The reason is presumed as follows.
That is, due to the hydrolysis and condensation reactions described below that the monomer undergoes, the number of OH groups is reduced, and branched, cyclic, and network structures are increased in the reaction composition, resulting in adsorption to the inorganic layered compound. This is because there is a tendency that the adhesiveness of the surface coating layer is lowered and the effect of improving the adhesion of the surface coating layer is impaired.
The proportion of polymers in the hydrolyzable silane composition is preferably 90% by mass or less. Below this upper limit, gelation tends to be difficult and storage stability tends to be high.
The ratio of the bifunctional hydrolyzable silane compound as a monomer in the hydrolyzable silane composition is preferably 10% by mass or more and 30% by mass or less.

Next, conditions for hydrolysis and condensation reactions will be described.
This reaction is carried out by continuously dropping the acid catalyst aqueous solution into the hydrophilic solvent solution in which the above hydrolyzable silane composition is dissolved under stirring conditions.

The hydrophilic solvent is not particularly limited as long as it can dissolve the polymer of the hydrolyzable silane compound, but generally alcohols such as methanol, ethanol, propanol and butanol, ethyl cellosolve, butyl cellosolve and propyl cellosolve. Glycols such as cellosolves such as ethylene glycol, propylene glycol and hexylene glycol are used. These solvents may be used alone or in combination of two or more.

The amount of the hydrophilic solvent used is not particularly limited, but is usually 0.1 to 100,000 parts by mass, preferably 100 to 10,000 parts by mass, per 100 parts by mass of the hydrolyzable silane composition.

Examples of the acid catalyst aqueous solution include aqueous solutions of hydrochloric acid, acetic acid, and the like. The hydrolysis and condensation reaction of the hydrolyzable silane compound can be carried out using only water without using an acid catalyst. is difficult to achieve. The reason is presumed as follows.
That is, when no catalyst is used, the reaction occurs near neutrality, and the hydrolysis reaction is very slow, but the condensation reaction proceeds rapidly. This is because a condensation reaction occurs and the molecular weight distribution of the product is widened. In addition, since the hydrolysis is insufficient and many unreacted alkoxy groups remain in the product, the storage stability of the silicate oligomer solution is poor and gelation may occur.

The acid concentration in the acid catalyst aqueous solution is usually in the range of 0.0001 to 0.1% by mass, preferably 0.001 to 0.01% by mass. When the acid catalyst is used as such a low-concentration aqueous solution, a large amount of water is entrained in the reaction system, making it easier to adjust the pH in the reaction system. can be suppressed. As a result, the OH groups generated by hydrolysis tend to disappear at an appropriate rate, making it easier to obtain a reaction composition rich in linear structure with a large amount of OH groups.

If the acid concentration of the acid catalyst aqueous solution is much lower than the above lower limit, it tends to be difficult to achieve the object of the present invention, as in the case where the reaction is carried out without using an acid catalyst. If the concentration of is higher than the above upper limit, the hydrolysis proceeds rapidly, but the condensation reaction is slow, so that only a reaction composition with a low molecular weight is obtained, and the effects of substrate adhesion and scratch resistance are dramatically reduced. trending downward.

The amount of the acid catalyst used is usually 0.001 to 10 millimoles, preferably 100 millimoles, per 100 moles of the total amount of hydrolyzable groups (typically alkoxy groups) in the hydrolyzable silane composition in the hydrophilic solvent solution. 0.01 to 10 millimoles.

The acid catalyst aqueous solution is dropped continuously, and the dropping speed is appropriately selected so that the temperature in the reaction system does not suddenly rise. The dropping rate of the acid catalyst aqueous solution is usually 1 to 10 ml/min, preferably 3 to 5 ml/min, per 100 ml of the hydrophilic solvent solution. The dropped catalyst aqueous solution is immediately and uniformly dispersed by stirring, and uniform hydrolysis is performed. In addition, the stirring method can employ the method employ|adopted by the normal chemical reaction.

The hydrolysis and condensation reactions of the hydrolyzable silane compounds in the hydrolyzable silane composition actually occur sequentially and in parallel. In a preferred embodiment of the present invention, from the viewpoint of obtaining a reaction composition rich in a linear structure having a large amount of OH groups, the following reaction is carried out so that hydrolysis and condensation reactions are carried out separately as much as possible. It is divided into three steps.

(1) Hydrolysis reaction step:
The hydrolysis reaction is performed by dropping the acid catalyst aqueous solution into the hydrophilic solvent solution of the hydrolyzable silane composition under stirring conditions. The reaction temperature is generally 5 to 50°C, preferably 10 to 40°C. If the reaction temperature is less than the above lower limit, the hydrolysis reaction becomes too slow, and if it exceeds the above upper limit, it becomes difficult to avoid the condensation reaction. The reaction temperature is controlled by the temperature and circulation amount of the coolant passed through the jacket of the reactor, the dropping speed of the acid catalyst aqueous solution, and the like. When the boiling point of the hydrophilic solvent is low, the hydrolysis reaction is carried out under reflux conditions. The reaction time is generally 1 to 60 minutes, preferably 5 to 30 minutes.

The hydrolysis reaction is an exothermic reaction, and the temperature of the reaction solution usually rises by 1 to 15°C. In order to confirm that the hydrolysis reaction is substantially completed, it is preferable to continue stirring until the reaction temperature drops by 5 to 10° C. after the dropwise addition of the aqueous acid catalyst solution is completed.

(2) Condensation reaction step:
Following the above steps, the reaction temperature is raised as necessary, and the condensation reaction is carried out under stirring conditions. The reaction temperature is generally 40-80°C, preferably 50-60°C. If the reaction temperature is less than the above lower limit, the condensation reaction becomes too slow, and if it exceeds the above upper limit, it becomes difficult to avoid excessive condensation reaction. The heating rate is usually 0.1 to 10° C./min. The reaction time is generally 1 to 120 minutes, preferably 5 to 60 minutes.

(3) Condensation reaction termination step:
The condensation reaction is stopped by cooling the reaction solution. The cooling temperature is usually 10-30°C. At this time, it is effective to stop the condensation reaction by cooling dilution by adding a solvent to reduce the concentration of the condensation reaction composition. The solvent is preferably the same as the reaction solvent, but another solvent may be used to adjust the liquid property.

The amount of the solvent to be added is usually in the range of 50 to 150% by mass when expressed as the concentration of the solvent with respect to the total amount of the hydrolyzable silane compound, the solvent used in the reaction and the aqueous acid catalyst solution.

According to the step of stopping the condensation reaction by cooling and dilution, the storage stability of the obtained silicate oligomer solution is improved, and it is possible to produce a silicate oligomer solution whose concentration can be adjusted to meet the requirements of each application.

The above condensation reaction step determines the weight average molecular weight of the resulting silicate oligomer. The weight average molecular weight of the silicate oligomer is generally 1,000-5,000, preferably 2,000-4,000. Such molecular weights correspond to multimers with an average degree of multimerization n of 2-100.

The above weight average molecular weight is a value measured by gel permeation chromatography (GPC) under the following conditions.
Solvent: Tetrahydrofuran Apparatus name: TOSOH HLC-8220GPC
Column: Used by connecting TOSOH TSKgel Super HM-N (2) and HZ1000 (1) Column temperature: 40°C
Sample concentration: 0.01% by mass
Flow rate: 0.6ml/min
Calibration curve: PEG (molecular weight 20000, 4000, 1000, 200 using a calibration curve by 4-point cubic approximation

The silicate oligomer concentration of the silicate oligomer solution thus obtained is preferably 15% by mass or less, more preferably 10% by mass or less, more preferably 5% by mass or less, and most preferably 3% by mass or less. If the concentration of the silicate oligomer is high, the stability of the solution deteriorates, and it is difficult to achieve uniform dispersibility when mixed with a dispersion liquid containing inorganic nanosheets, which will be described later. On the other hand, the silicate oligomer concentration of the silicate oligomer solution is preferably 0.1% by mass or more from the aspect of shape efficiency of the surface coating layer.

<Inorganic layered compound>
The inorganic layered compound used in the present invention is preferably a smectite clay mineral from the viewpoint of preventing permeation into the porous body, and the smectite clay mineral can be used by dispersing it in a dispersion medium.

Smectite group clay minerals include montmorillonite, saponite, hectorite, stevensite, and beidellite. It is a nanomaterial having a thin plate-like high-aspect structure and a large specific surface area, and montmorillonite is particularly preferably used.

A smectite group clay mineral is expanded and cleaved by being mixed with a dispersion medium, and formed into a two-dimensional nanomaterial (hereinafter sometimes referred to as "inorganic nanosheet") separated from one layer to several layers. can be used.

There are natural and synthetic smectite clay minerals, but some natural products are colored due to the ingredients contained in them, so when used for optical materials, synthetic substances with no coloring and high transparency are recommended. preferred. Sumecton ST, Sumecton SWN, Sumecton SA, etc. manufactured by Kunimine Industries Co., Ltd. can be used as commercial products of the synthetic product.

Although the shape of the inorganic nanosheet is not limited, it is preferable that the area in the plane direction is larger than the pore size of the porous material to be coated. A shape with a small area has a problem of penetrating into the pores during coating and clogging the pores. Therefore, dispersion using a high-pressure dispersing device or a high-speed stirring device, which imposes a high load, is not suitable for reducing the size of the inorganic nanosheets.

Water is preferably used as the dispersion medium, and water alone or a mixed solvent of water and a hydrophilic solvent may be used. Alcohols such as methanol, ethanol and propanol are used as the hydrophilic solvent in order to improve the wettability of the coating liquid for forming the surface coating layer on the porous body. The type of solvent that can be mixed is not limited as long as it does not inhibit the dispersion of the inorganic nanosheets. However, if a solvent other than water is used, the dispersion state of the coating liquid becomes unstable as the ratio increases.

A dispersion containing inorganic nanosheets can be obtained by adding powder of an inorganic layered compound to water and stirring the mixture. At this time, it is preferable to add the inorganic layered compound little by little, and after the added powder is dispersed transparently, the remaining powder is added. If all the powder is added at once, the powder may remain because it cannot be dispersed.

The concentration of the inorganic nanosheets in the dispersion liquid of the inorganic nanosheets is preferably 5% by mass or less, more preferably 3% by mass, and more preferably 2% by mass. If the concentration of the inorganic nanosheet exceeds 5% by mass, poor dispersion and viscosity increase are likely to occur, making it difficult to obtain a surface coating layer that is thin, smooth, and highly effective in preventing permeation. On the other hand, from the viewpoint of formation efficiency of the surface coating layer, the inorganic nanosheet concentration in the inorganic nanosheet dispersion is preferably 0.1% by mass or more.

<Method for producing coating solution for forming surface coating layer>
Next, a method for producing a surface coating layer-forming coating liquid according to an embodiment of the present invention will be described.
The coating liquid for forming the surface coating layer is obtained by mixing a dispersion liquid containing an inorganic layered compound, preferably the inorganic nanosheets described above, and the silicate oligomer solution described above.

When mixing the dispersion and the silicate oligomer solution, a hydrophilic solvent such as an alcohol may be added as necessary. It is possible to improve the film formability by adjusting the solid content concentration of the liquid and adjusting the wettability of the coating liquid to the porous body.

The mixing ratio of the inorganic layered compound and the silicate oligomer when mixing the dispersion liquid of the inorganic layered compound and the silicate oligomer solution was determined by forming a surface coating layer on the porous body using the resulting coating liquid for forming a surface coating layer. In practice, there are no particular restrictions as long as the pores of the porous body are not clogged. If the proportion of the silicate oligomer is too high, the amount of silicate oligomer that is not adsorbed to the layered inorganic compound increases, causing a problem of penetration during coating. On the other hand, if the amount of the silicate oligomer is too small, the inorganic layered compound to which the silicate oligomer is not adsorbed increases, and the adhesion between the inorganic layered compounds and between the surface coating layer and the porous body becomes low. Layers may delaminate.
From such a viewpoint, the mixing ratio of the inorganic layered compound and the silicate oligomer is preferably inorganic layered compound: silicate oligomer = 1:0.1 to 10 (mass ratio), particularly 1:0.2 to 1 (mass ratio). mass ratio).

Hydrophilic solvents such as alcohols can be added in an amount such that the inorganic layered compound does not aggregate, and may be added to the dispersion of the inorganic layered compound, may be added to the silicate oligomer solution, or may be added to the dispersion of the inorganic layered compound. and the silicate oligomer solution, or may be added at the time of mixing.

The coating liquid for forming the surface coating layer is preferably adjusted so that the solid content concentration (concentration of components other than the solvent) is 0.1 to 5% by mass, particularly 0.1 to 3% by mass. If the solid content concentration of the coating solution for forming the surface coating layer is below the above upper limit, the coating solution tends to be difficult to gel. Yes and preferred.

The reason why the coating solution for forming the surface coating layer of the present invention is produced by mixing the silicate oligomer solution and the inorganic stratiform compound dispersion as described above is as follows.
Silicate oligomers have a small molecular size, and if used as they are, they will permeate into the pores of the porous body and clog the pores.
The silicate oligomer obtained by the above-described production method is a reaction composition rich in linear chain structure with a large amount of OH groups, and is stabilized in a hydrophilic solvent. When mixed in solution, the OH groups are reduced by a condensation reaction. On the other hand, since the dispersion of the inorganic layered compound is alkaline, the OH groups are rapidly condensed by mixing the silicate oligomer solution and the dispersion of the inorganic layered compound, and some of them are adsorbed on the surface of the inorganic layered compound. It is presumed that some of them are condensed between silicate oligomers. Here, the state of adsorption can be observed by measuring and comparing the ¹ H-NMR of the silicate oligomer solution and the dispersion obtained by adding the inorganic layered compound to the silicate oligomer solution. That is, a chemical shift value (δ value) presumed to be an OH group is observed at 6 to 8 ppm by ¹ H-NMR measurement of a silicate oligomer solution, and a dispersion obtained by adding an inorganic layered compound to this solution has a peak at 6 to 8 ppm. disappears, it is presumed that the silicate oligomer and the inorganic layered compound were adsorbed.
Therefore, the above production method allows the silicate oligomer to be adsorbed on the layered inorganic compound, and furthermore, allows storage in a solvent in a transparent and stable state. By applying the coating solution for forming the surface coating layer to the surface of the porous body in this state, it is possible to form a surface coating layer of the inorganic layered compound on the surface with good adhesion while maintaining the pores of the porous body. can.
The term "adsorption" as used in the present invention may be either chemical adsorption or physical adsorption, and includes binding by interactions such as hydrogen bonding, ionic bonding, covalent bonding, and van der Walls force. Among them, interaction by hydrogen bond, ionic bond and covalent bond is preferable. In the above embodiment, it is believed that the adsorption is partly due to ionic interaction and partly due to condensation reaction.

<Formation of surface coating layer>
The surface coating layer of the present invention can be formed on the porous body by coating the surface of the porous body with the coating solution for forming the surface coating layer, heating, and drying to remove the solvent.

The coating method of the coating liquid for forming the surface coating layer is not particularly limited, and includes dip coating, spin coating, die coating, spray coating, gravure coating, roll coating, curtain coating, screen printing, Inkjet printing methods may be mentioned.

The above drying is carried out to remove the solvent, the drying temperature is usually 70 to 120° C., and a hot air dryer or the like is preferably used. The drying time is usually 1 to 10 minutes, preferably 1 to 5 minutes.

The film thickness of the surface coating layer is preferably 1 to 30 nm, more preferably 1 to 20 nm. If the film thickness of the surface coating layer is too thick, an increase in the minimum reflectance and a shift in the minimum reflectance wavelength occur in the antireflection performance, which may cause problems in terms of optical performance. On the other hand, if the film thickness of the surface coating layer is too thin, there is a possibility that the permeation prevention performance due to the formation of the surface coating layer may be insufficient.

[Porous silicon laminate]
As described above, for example, by forming the surface coating layer of the present invention on a porous silicon layer formed on a substrate by the method for producing a porous silicon layer described above, as shown in FIG. A porous silicon laminate of the porous silicon layer 2/surface coating layer 3 can be obtained.

In the porous silicon laminate of the present invention in which the surface coating layer of the present invention is formed on a porous body, the fact that the pores of the porous body are not blocked by the formation of the surface coating layer is It can be confirmed by measuring the minimum reflectance.
That is, when the pores of the porous body are filled by forming the surface coating layer, the refractive index increases, and as a result, the minimum reflectance becomes larger than that of the porous body before the formation of the surface coating layer.
When a surface coating layer is formed on the surface of a porous silicon body using the coating liquid for forming a surface coating layer of the present invention, the degree of increase in minimum reflectance is small compared to the porous silicon body before the formation of the surface coating layer. , the rate of increase is preferably less than 1.0%, more preferably 0.8% or less.
The minimum reflectance of the porous silicon laminate of the present invention is preferably less than 1.5%, more preferably 1.0% or less.

Here, the minimum reflectance refers to the reflectance at the wavelength of light at which the reflectance is minimum among the reflectance at a specific wavelength in the wavelength range of 200 to 1500 nm, and the surface coating layer side of the porous silicon laminate. It can be obtained from the reflection spectrum measured by letting light enter from the
The minimum reflectance of the porous silicon layer varies depending on the refractive index (porosity) of the porous silicon layer and the substrate to be coated. The minimum reflectance is about 0.05% with a porous silicon layer, and about 0.5% with a porous silicon layer having a refractive index of 1.32.

Porous silicon laminates are required to have resistance to scratches and fingerprints in addition to chemical resistance, which poses problems such as permeation, as shown in FIG. The surface can be hydrophobized by forming a surface treatment layer 4 on the surface coating layer 3 of 2 using a fluorine-based silane coupling agent or an alkyl-based silane coupling agent. In this case, in the porous silicon body not formed with the surface coating layer of the present invention, the material enters the pores of the porous silicon layer to increase the refractive index and further reduce the mechanical strength of the porous silicon layer. There's a problem. On the other hand, in the porous silicon laminate of the present invention, since the surface coating layer is provided on the surface of the porous silicon layer, there is no problem caused by the infiltration of the surface treatment agent such as the silane cupping agent. , can be surface treated. The surface-treated porous silicon laminate obtained here has a smooth surface and a hydrophobized surface, so that the scratch resistance and stain resistance are improved, and fingerprints can be wiped off.

Such a porous silicon laminate of the present invention can be effectively used, for example, as electronic materials such as displays, antireflection films such as solar cells, and light guide plates.

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

[Example 1]
[Preparation of porous silicon laminate]
<Production of silicate oligomer>
(1) Hydrolysis reaction step:
In a 500 mL jacketed reactor, 5 parts by mass of product "KBM22" (dimethyldimethoxysilane content 99% by mass) manufactured by Shin-Etsu Silicone Co., Ltd., product "Silicate MS51" manufactured by Mitsubishi Chemical Corporation (average degree of multimerization n: 7, methyl silicate 20 parts by mass of oligomer content 99.8% by mass) and 50 parts by mass of ethanol are charged, the upper reaction temperature is set to 40° C., and 33 parts by mass of a 0.007% by mass hydrochloric acid aqueous solution is added dropwise over 10 minutes under stirring conditions. bottom. At this time, the exothermic reaction raised the reaction temperature by 5-10°C. Stirring was continued until the reaction temperature dropped by 5-10°C. The ratio of the polymer in the bifunctional hydrolyzable silane compound (the ratio of "silicate MS51" to the total amount of "KBM22" and "silicate MS51") was 80% by mass.

(2) Condensation reaction step:
After the hydrochloric acid aqueous solution was added dropwise, the temperature was raised to 60°C over 30 minutes under stirring conditions, and the temperature was maintained at 60°C for 30 minutes. After that, it was cooled to room temperature.

(3) Condensation reaction termination step:
After cooling, 110 parts by mass of ethanol was mixed and stirred for 30 minutes to obtain 218 parts by mass of a silicate oligomer solution (A). The silicate oligomer concentration of this silicate oligomer solution (A) is 7% by mass.

<Preparation of Inorganic Layered Compound Dispersion>
1 part by mass of "Smecton SWN" (synthetic smectite) manufactured by Kunimine Industries Co., Ltd. was added in several batches to 99 parts by mass of pure water under stirring, and stirred and mixed for 30 minutes to disperse the inorganic layered compound at a concentration of 1% by mass. 100 parts by mass of liquid (B) was obtained.

<Production of coating solution for forming surface coating layer>
To 218 parts by mass of the silicate oligomer solution (A) obtained above, 3612 parts by mass of the inorganic layered compound dispersion (B) obtained above and 1335 parts by mass of ethanol were added and mixed with stirring to form a surface coating layer. 5165 parts by mass of the forming coating liquid was obtained. The ratio of the inorganic layered compound to the silicate oligomer contained in this coating solution for forming the surface coating layer was inorganic layered compound:silicate oligomer = 1:0.43 (mass ratio), and the solid content concentration was 1% by mass.

<Preparation of porous silicon laminate>
The surface coating layer obtained above was formed on the surface of a porous silicon layer (porosity 29%, thickness 132 nm) having a refractive index of 1.32 formed on a 1 mm thick slide glass plate ("S9111" manufactured by Matsunami Glass Co., Ltd.). for 30 seconds at 1500 rpm with a spin coater ("MS-A150" manufactured by Mikasa). C. for 1 minute to obtain a porous silicon laminate (C) having a surface coating layer laminated thereon.
When the pore size of the porous silicon layer having a refractive index of 1.32 was measured by analyzing an image observed with an electron microscope, it was confirmed to be 50 nm or less.

[Evaluation of porous silicon laminate]
<Evaluation of Adhesion between Porous Silicon Layer and Surface Coating Layer>
A 24 mm cellophane tape for industrial use manufactured by Nichiban Co., Ltd. was attached to the surface of the porous silicon laminate (C) obtained above, and separated vertically, and the adhesion between the porous silicon layer and the surface coating layer was measured according to the following criteria. evaluated.
(Evaluation criteria for adhesion)
○: Those that do not peel between layers ×: Those that peel between layers

<Evaluation of Penetration of Porous Silicon Laminate>
In the porous silicon laminate (C) obtained above, the reflectance when light is incident on the laminate before and after the formation of the surface coating layer from the surface coating layer side is measured. The state of penetration into the pores of the porous silicon layer due to the application of the coating liquid was evaluated. In order to suppress the reflection from the back surface of the glass substrate, the laminate sample to be evaluated was prepared by attaching Denka's vinyl tape (black) to the back surface, and the reflection was performed by Filmetrics Co.'s interferometric film thickness measurement device F20. Spectra were measured to determine the minimum reflectance.
Incidentally, the minimum reflectance of the laminated body in which a porous silicon layer having a refractive index of 1.32 was formed on a glass substrate was 0.5%. If penetration into the pores of the porous silicon layer occurs, the refractive index of the porous silicon layer increases, resulting in a higher minimum reflectance.

Table 1 shows the above evaluation results.

[Comparative Example 1]
A porous silicon laminate was produced and evaluated in the same manner as in Example 1, except that no silicate oligomer was used. Table 1 shows the results.

[Comparative Example 2]
A porous silicon laminate was produced and evaluated in the same manner as in Example 1, except that the inorganic layered compound was not used. Table 1 shows the results.

Table 1 shows the following.
In Example 1, the adhesion between the surface coating layer of the inorganic layered compound to which the silicate oligomer was adsorbed and the surface of the porous silicon layer was excellent, and the reflectance of the porous silicon laminate was less than 1.5%.
On the other hand, in Comparative Example 1, since only the inorganic layered compound was laminated, there was no adhesion between the surface coating layer and the porous silicon layer. From this, it can be said that the silicate oligomer component is essential for the adhesion to the porous body.
In Comparative Example 2, although the adhesion is good, the minimum reflectance is 1.5% or more, and the silicate oligomer penetrates into the pores of the porous silicon layer, which is the original porous silicon layer. It can be said that the performance of

[Example 2]
[Preparation of porous silicon body/glass substrate laminate]
In Example 1, the The resulting coating liquid for forming a surface coating layer was dropped and coated with a spin coater (“MS-A150” manufactured by Mikasa Co., Ltd.) at 1500 rpm for 30 seconds. (manufactured by Yamato Scientific Co., Ltd.) and dried at 120° C. for 1 minute to obtain a porous silicon laminate having a surface coating layer laminated thereon.

A commercially available optical adhesive sheet (“CS98641UA” by NITTO) is attached to the surface of the surface coating layer of the porous silicon laminate obtained above, and the surface coating layer of the porous silicon laminate is sandwiched through the optical adhesive sheet. A slide glass plate was pasted on.
Next, by peeling off the release PET film, a laminate (D) having a laminated structure of glass substrate/optical adhesive sheet/surface coating layer/porous silicon layer was obtained from the glass substrate side.

[Evaluation of porous silicon body/glass substrate laminate]
<Evaluation of Adhesion between Porous Silicon Layer and Surface Coating Layer>
In the production of the laminate (D), after peeling off the release PET film, if the porous silicon body does not remain on the release PET film side, the adhesion is good "○" (the porous silicon layer is an optical adhesive The porous silicon body remained on the release PET film side) was evaluated as poor adhesion "x" (the surface coating layer was transferred to the optical adhesive side, remained on the release PET film).

<Evaluation of Penetration of Porous Silicon/Glass Substrate Laminate>
The penetration state of the optical pressure-sensitive adhesive into the pores of the porous silicon layer was evaluated by measuring the reflectance when light was incident on the laminate (D) obtained above from the glass substrate side. . For the laminate (D) to be evaluated, in order to suppress the reflection from the back surface (porous silicon layer side) of the laminate (D), a vinyl tape (black) manufactured by Denka Co., Ltd. was attached to the back surface. The reflection spectrum was measured with an interferometric film thickness measuring device F20 manufactured by Metrics to determine the minimum reflectance.
Incidentally, the minimum reflectance of the laminated body in which a porous silicon layer having a refractive index of 1.32 was formed on a glass substrate was 0.5%. When the optical adhesive penetrates into the pores of the porous silicon layer, the refractive index of the porous silicon layer increases, resulting in a higher minimum reflectance.
In addition, the sample subjected to the above penetration evaluation was stored at 70° C. for 30 minutes, and then the minimum reflectance was measured again in the same manner.

Table 2 shows the above evaluation results.

[Comparative Example 3]
A porous silicon body/glass substrate laminate was produced in the same manner as in Example 2, except that the coating liquid for forming the surface coating layer was not used, and the evaluation was performed in the same manner. Table 2 shows the results.

[Comparative Example 4]
A porous silicon/glass substrate laminate was produced and evaluated in the same manner as in Example 2, except that no silicate oligomer was used. In addition, since the laminate of this comparative example had poor adhesiveness, the penetration property was not evaluated. Table 2 shows the results.

Table 2 reveals the following.
In Example 2, the adhesion between the surface coating layer using the silicate oligomer and the inorganic stratiform compound and the surface of the porous silicon layer was good, and the laminate had a reflectance of 1.0% or less, 70°C, 30°C. There was no change in minute retention.
On the other hand, in Comparative Example 3, the laminate had a reflectance of 1.0% or more, and a change in reflectance was observed when the laminate was held at 70° C. for 30 minutes. It can be said that this is due to the fact that since there is no surface coating layer on the surface of the porous silicon layer, the component of the optical pressure-sensitive adhesive permeates into the pores of the porous silicon layer, thereby increasing the reflectance.
In Comparative Example 4, the porous silicon layer remained on the release PET film side. In other words, it can be said that only the inorganic layered compound migrated to the optical pressure-sensitive adhesive side due to the lack of adhesion between the porous silicon body and the inorganic layered compound.

REFERENCE SIGNS LIST 1 substrate 2 porous silicon layer 3 surface coating layer 4 surface treatment layer

Claims (7)

A coating liquid for forming a coating layer on the surface of a porous body that is any of a porous silicon body, a porous metal, or a porous inorganic-organic hybrid body, comprising a smectite group clay mineral to which a silicate oligomer is adsorbed. and a coating solution for forming a surface coating layer, wherein the mass ratio of the smectite clay mineral and the silicate oligomer is smectite clay mineral :silicate oligomer=1:0.2-1. A method for producing a coating liquid for forming a coating layer on the surface of a porous body that is one of a porous silicon body, a porous metal, and a porous inorganic-organic hybrid, comprising:
In a hydrophilic solvent solution in which a hydrolyzable silane composition containing a bifunctional hydrolyzable silane compound and a polymer of a hydrolyzable silane compound and containing 50% by mass or more of the polymer of the hydrolyzable silane compound is dissolved, Under stirring, an acid catalyst aqueous solution having an acid concentration of 0.0001 to 0.01% by mass is continuously added dropwise to perform hydrolysis and condensation reactions of the hydrolyzable silane composition,
Diluting the resulting reaction solution with a solvent to obtain a silicate oligomer solution,
The obtained silicate oligomer solution and the dispersion in which the smectite group clay mineral inorganic layered compound was dispersed in the dispersion medium were mixed so that the mixing ratio of the smectite group clay mineral and the silicate oligomer was 1:0. A method for producing a coating solution for forming a surface coating layer, characterized by mixing so as to have a ratio of 2 to 1 (mass ratio). A surface coating comprising a porous silicon body and a smectite group clay mineral to which a silicate oligomer is adsorbed, wherein the mass ratio of the smectite group clay mineral to the silicate oligomer is 1:0.2 to 1:0.2 to 1. A porous silicon laminate obtained by laminating a layer. 4. The porous silicon laminate according to claim 3 , wherein the porous silicon body has a pore size of 50 nm or less. In terms of the minimum reflectance for light incident on the porous silicon laminate from the surface coating layer side, the difference between the minimum reflectance before and after forming the surface coating layer is less than 1.0%. 5. The porous silicon laminate according to claim 3 or 4 . 6. The porous silicon laminate according to any one of claims 3 to 5 , wherein the surface of said surface coating layer is treated with a silane coupling agent. 7. A method for producing a porous silicon laminate according to any one of claims 3 to 6 , wherein the smectite group clay mineral having silicate oligomers adsorbed on the surface of the porous silicon body having a pore size of 50 nm or less. A method for producing a porous silicon laminate, comprising a step of applying a coating solution for forming a surface coating layer containing and then drying.

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